Coccolith biomineralisation studied with atomic force microscopy

Henriksen, Karen Friis; Young, Jeremy R.; Bown, Paul R.; Stipp, S. L. S.

doi:10.1111/j.0031-0239.2004.00385.x

Cited by 53 publications

(49 citation statements)

References 14 publications

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“…For consideration, the mass of a 30-nm thick organic coating covering an area of about 300 μm 2 would be approximately 10 pg. Such a protective layer is consistent with evidence of organic coatings on cultured coccoliths presented by Henriksen et al (7). The material remaining after dissolution of fossil coccoliths lacked form and was difficult to differentiate from the glue on the cantilever, but comparing Fig.…”

Section: Resultssupporting

confidence: 89%

“…Algae form the individual crystals they need for making coccoliths on templates of complex sugars (4)(5)(6)(7). Polysaccharides extracted from cultured algae inhibit calcite growth by blocking some crystal surface sites (8) and mature coccoliths are protected from dissolution by an organic coating (7).…”

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confidence: 99%

“…Polysaccharides extracted from cultured algae inhibit calcite growth by blocking some crystal surface sites (8) and mature coccoliths are protected from dissolution by an organic coating (7). Previous work has also suggested the presence of organic material associated with coccoliths from chalk (9)(10)(11).…”

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confidence: 99%

“…In ancient material, the proteins are assumed to have been eaten millions of years ago when the algae sank to the ocean floor, so proteins are not a problem, but chalk invariably also contains quartz, flint, clay, and fossils of other microorganisms. Although single coccoliths have been studied previously (7,12,13), dissolution rates To whom correspondence may be addressed. E-mail: tue@nano.ku.dk or stipp@ nano.ku.dk.…”

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confidence: 99%

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Tracking single coccolith dissolution with picogram resolution and implications for CO ₂ sequestration and ocean acidification

Hassenkam

Johnsson

Bechgaard

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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Coccoliths are micrometer scale shields made from 20 to 60 individual calcite (CaCO 3 ) crystals that are produced by some species of algae. Currently, coccoliths serve as an important sink in the global carbon cycle, but decreasing ocean pH challenges their stability. Chalk deposits, the fossil remains of ancient algae, have remained remarkably unchanged by diagenesis, the process that converts sediment to rock. Even after 60 million years, the fossil coccolith crystals are still tiny (<1 μm), compared with inorganically produced calcite, where one day old crystals can be 10 times larger, which raises the question if the biogenic nature of coccolith calcite gives it different properties than inorganic calcite? And if so, can these properties protect coccoliths in CO 2 challenged oceans? Here we describe a new method for tracking dissolution of individual specimens, at picogram (10 −12 g) resolution. The results show that the behavior of modern and fossil coccoliths is similar and both are more stable than inorganic calcite. Organic material associated with the biogenic calcite provides the explanation. However, ancient and modern coccoliths, that resist dissolution in Ca-free artificial seawater at pH > 8, all dissolve when pH is 7.8 or lower. Ocean pH is predicted to fall below 7.8 by the year 2100, in response to rising CO 2 levels. Our results imply that at these conditions the advantages offered by the biogenic nature of calcite will disappear putting coccoliths on algae and in the calcareous bottom sediments at risk. marine carbon cycle | ocean buffer capacity | dissolution rate | atomic force microscopy | single particle dissolution

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Section: Resultssupporting

confidence: 89%

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confidence: 99%

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confidence: 99%

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confidence: 99%

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Tracking single coccolith dissolution with picogram resolution and implications for CO ₂ sequestration and ocean acidification

Hassenkam

Johnsson

Bechgaard

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

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“…Fourier Transform Infrared Spectroscopy (FTIR) experiments showed evidence of peaks in the FTIR spectrum, indicating that hydroxyl species were present on the surface in bulk water [13]. However, previous ab-initio calculations [9] investigated Helicosphera carteri [5] a water configuration where one dissociated H 2 O was initially placed above each Ca ion on the calcite {1014} surface. The dissociated H 2 O molecules spontaneously re-associated on the surface during static relaxation calculations, implying that the dissociated state is unstable.…”

Section: Modelsmentioning

confidence: 99%

Investigation of the Interaction of Water with the Calcite (10.4) Surface Using Ab Initio Simulation

2009

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Density functional theory calculations were employed to explore the interaction between water and the {1014} surface of calcite. In addition a defective {1014} surface and stepped surfaces in contact with water were investigated. A series of percentage water coverages and water configurations were explored, including dissociated water states. Static relaxations found associated water to be favourable on the {1014} surface, although a metastable dissociated state 1.77eV higher in energy was found.Molecular dynamics (MD) simulations of low water coverage reveal fluctuations in the H-O water bond when the H atom is directed towards a surface CO 3 ion. Desorption of an H 2 O molecule was observed in simulations above 900K. Water was found to be strongly bound to the perfect {1014} surface, with an adsorption energy of -0.91eV. MD simulations of a defective {1014} surface found water to favour dissociation at CO 3 vacancies. However, water at Ca vacancies diffused across the surface to form a bond with the nearest surface Ca ion. Water was also found to favour an associated state at both acute and obtuse steps. On all these imperfect surfaces water was found to adsorb strongly to the surface, with adsorption energies ranging from -0.99eV to -1.60eV.

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Structural Control of Crystal Nuclei by an Eggshell Protein

et al. 2010

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The use of biomolecules in nature to direct crystal growth leads to a degree of polymorph and morphology control that far surpasses anything currently accessible in a laboratory. Examples include the intricate nano-and microcrystalline structures found in mollusk shells, [1] coccoliths, [2] and eggshells, [3] which imbue the shells with important physical properties. Recent work has exploited biomolecules [4,5] and biomimetic processes [6,7] to fabricate new materials, but the scope for this would be greatly enhanced if the mechanism by which the biomolecules effect this control were better understood. Molecular simulation should be an ideal tool for identifying these mechanisms. Methods have been developed to model the clustering of inorganic ions on biomolecules, [8] but simulating the onset of long-range crystalline order in the inorganic deposit due to the biomolecule has not been possible. Crystal nucleation, a crucial step in polymorph selection, occurs on timescales that have hitherto been inaccessible to molecular simulation. Herein, we show that our recent developments to metadynamics, [9,10] coupled with the latest generation of leadership-class computing, have now made it possible to simulate the role of a native protein in controlling the onset of mineral crystallization. We illustrate this process with the first molecular simulation of spontaneous crystallization of amorphous CaCO 3 in the presence of the chicken eggshell protein ovocleidin-17 (OC-17).Eggshells have an intricate structure that consists of two domains attached to an inner membrane. [11] The first domain is an array of small polycrystalline calcite clusters (mammillary caps) attached to the membrane that surrounds the albumin; the second domain (pallisade layer) consists of elongated calcite crystals with partial alignment. Experiments have identified various proteins associated with eggshell formation. One class, C-type lectin-type proteins, is found only within the mineral region and is important in controlling calcite deposition. [12] In vitro studies with OC-17 (chicken) and ansocalcin (goose) have shown that these proteins promote calcite formation and define the crystal morphology. [13][14][15] There is now much experimental evidence that many biominerals, [16] including eggshells, [17] begin as nanoparticle deposits of an amorphous inorganic material. Our recent simulations [10] support this, showing amorphous calcium carbonate (ACC) to be energetically stable, even at larger particle sizes where calcite becomes thermodynamically preferred. The interaction between OC-17 and ACC particles of various sizes is therefore likely to be fundamental to the mechanism by which OC-17 controls calcite growth, and so forms the focus of the work described herein.Simulations [18] were performed using metadynamics (metaD). [19,20] MetaD extends conventional molecular dynamics (MD) to sample the free-energy landscape in terms of collective coordinates (that is, order parameters or reaction coordinates). It is particularly good at finding the rar...

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Coccolith biomineralisation studied with atomic force microscopy

Cited by 53 publications

References 14 publications

Tracking single coccolith dissolution with picogram resolution and implications for CO ₂ sequestration and ocean acidification

Tracking single coccolith dissolution with picogram resolution and implications for CO ₂ sequestration and ocean acidification

Investigation of the Interaction of Water with the Calcite (10.4) Surface Using Ab Initio Simulation

Structural Control of Crystal Nuclei by an Eggshell Protein

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Coccolith biomineralisation studied with atomic force microscopy

Cited by 53 publications

References 14 publications

Tracking single coccolith dissolution with picogram resolution and implications for CO 2 sequestration and ocean acidification

Tracking single coccolith dissolution with picogram resolution and implications for CO 2 sequestration and ocean acidification

Investigation of the Interaction of Water with the Calcite (10.4) Surface Using Ab Initio Simulation

Structural Control of Crystal Nuclei by an Eggshell Protein

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Tracking single coccolith dissolution with picogram resolution and implications for CO ₂ sequestration and ocean acidification

Tracking single coccolith dissolution with picogram resolution and implications for CO ₂ sequestration and ocean acidification